1. Field of the Invention
The present invention relates to a method for manufacturing a measuring diaphragm for gasmeters. More particularly, the present invention relates to a method of preparation of gas diaphragms, wherein the gasmeter is conveniently utilized in household applications and has a high measurement accuracy.
2. Prior Art
A gasmeter which measures the accumulated volume of gas passing through the gasmeter by counting the number of movements of a measuring diaphragm in the instrument as shown in FIG. 1 through FIG. 4 has been known.
The gasmeter comprises a pair of measuring vessel and also a pair of measuring diaphragm. When the pressure of gas at the outlet of the vessel is decreased by the consumption of gas, additional gas is introduced to the vessel through the inlet by the pressure of the supply gas and the measuring diaphragm is pushed to a side. The accumulated volume of the passing gas through the instrument is measured by counting number of the movement of the measuring diaphragm.
The mechanism of the measurement is explained in more detail in the following. Valves A and A' equipped to the instrument open or close the inlets of gas by moving sideways in connection with the movements of the diaphragm. In the example shown in FIG. 1, the valve A opens an inlet B connected to the right side of the diaphragm in the right vessel C. The gas in the left side of the diaphragm in the vessel can go to the line of utilization through another inlet D, an outlet E, and a connection K. At this time, the other valve A' closes inlets B' and D' and an outlet E'.
When gas in the left side of the measuring diaphragm F in the measuring vessel C is consumed, the pressure of the gas is decreased and a stream of gas is introduced to the right side of the diaphragm, pushing the diaphragm toward the left wall of the vessel with the pressure of the supply gas.
The stream of the incoming gas continues to push the diaphragm toward the left wall. When the diaphragm moves to a position almost in contact with the wall, the gas in the right side of the diaphragm is utilized through the outlet E which is opened by the shift of the valve A and then through the connection K.
The instrument has a cam L which rotates in connection with the two diaphragms F and F' as shown in FIG. 5. When the positions of valves A and A' are shifted from the positions shown in 1 to the positions shown in 2 automatically by the action of cam L, the connection in the gasmeter is changed to the one shown in FIG. 2. Thus, the gas in the left vessel is connected to the line of utilization and to the line of supply.
In the condition shown in FIG. 2, stream of gas is introduced into the vessel C' through the inlet B'. The gas newly introduced is accumulated in the left side of the measuring diaphragm F' and the gas previously accumulated in the right side of the diaphragm is discharged through the out let E'.
When the measuring diaphragm F' is pushed to the position almost in contact with the right wall of the vessel C', the positions of the valves A and A' are shifted from the positions shown in 2 of FIG. 5 to the position shown in 3 of FIG. 5 automatically by the action of cam L. Thus, the condition of the vessel is changed to the one shown in FIG. 3, a stream of gas is introduced into the vessel C through the inlet D and pushes the diaphragm F toward the right wall this time and the gas accumulated in the vessel C during the process shown in FIG. 1 is discharged through the outlet E and the connection K. When the process shown in FIG. 3 is finished, the positions of the valves are shifted by the action of the cam L from the positions shown in 3 of FIG. 5 to the positions shown in 4 and the condition of the vessel is changed to the one shown in FIG. 4. A stream of gas is introduced in the right side of the diaphragm, the accumulated gas in the left side of the diaphragm is discharged and a cycle of the process is finished.
When the utilization of gas is continued, a stream of gas continues to flow into the gasmeter through repeating of the processes shown in FIG. 1 through FIG. 4. The number of the repeated movement of the measuring diaphragm during the process is counted by the number of rotation of cam L connected to the diaphragm or by any other appropriate methods and the total volume of the gas passed through the gasmeter is measured.
When the utilization of gas is stopped, the pressure of gas at the outlet is increased and the movement of the diaphragm stops when the pressure at both sides of the diaphragm comes to balance.
This type of gasmeter has been widely used because it is conveniently utilized to household applications and reliable with highest accuracy of the measurement.
A cycle of the movement of the valves A and A' is monitored through the rotation of cam L which is connected to two measuring diaphragms. The number of the movement of the diaphragms is counted by counting the number of rotation of the link with the use of an accumulating counter and the accumulated count gives the volume of the gas passed through the gasmeter by a suitable calculation.
A measuring diaphragm utilized in a gasmeter of the type described here is, for example, a flexible diaphragm made of a sheet of a rubber-coated fabric having precise dimensions. The diaphragm is generally prepared to the same shape as the wall of the vessel as shown in FIG. 6.
The measuring diaphragm is shaped by using molds having a truncated cone shape or a truncated pyramid shape. A flat part is formed at the center and fixed to the shape by attaching two thin plates of a metal or a plastics in a sandwich structure. The periphery of the central flat part is made flexible. When the central flat part moves to the other side, the peripheral part is deformed to take an inversed shape and fits the wall of the vessel.
When, for example, the diaphragm is shaped to a truncated cone or pyramid to fit the left wall of the vessel, the diaphragm fits the wall well when it moves toward the left wall. However, when the diaphragm moves toward the right wall of the vessel, a loosely deformed shape Q is formed in the peripheral part of the diaphragm as shown in FIG. 1 through FIG. 4.
When the loosely deformed shape is formed, resistance to the direction of movement takes place because of the resilient effect of the shape formed in a different shape. Thus, smooth movement of the diaphragm is disturbed.
When the diaphragm is shaped to a truncated cone or pyramid to fit the left wall of the vessel like the above example, the diaphragm does not fit the right wall of the vessel in the same way as it does the left wall of the vessel.
These factors described here cause difference in movement of the diaphragm between the movement toward the left wall and the movement toward the right wall and further cause an error in the accumulated volume of gas measured by the gasmeter.
The effect of the shape is generally different between each piece of the diaphragm because the history during the molding is generally different between the pieces. This makes further cause of error in the measurement.
It is often observed that a diaphragm having a kind of shape effect acquires another kind of shape effect by numerous repeated movement during a prolonged period of usage. This causes an error in the measurement because the measured volume is often different from the volume at the time of approval testing.
A material which can easily follow the change in pressure, such as a single layer elastomeric sheet, may be used to avoid the effect of a molded shape. However, in this case, the diaphragm is easily extended to give a larger surface area, reproducibility of the movement of the diaphragm is decreased and the measurement of the volume of gas becomes less accurate.